I love the zombie apocalypse survival horror computer game Left 4 Dead. Which is a bit weird, considering zombies as a whole scare the snot out of me, and I avoid horror movies like the plague.
But Left 4 Dead has such awesome gameplay. Particularly the way it forces the players to work together and help each other out. For those who don't know, in Left 4 Dead, various things can incapacitate you: being mobbed by normal infected, the special attacks of most of the special infected, falling off a ledge, that sort of thing. The only way to cease being incapacitated is for one of your teammates to help you up, or do some similar action. Actually dying in L4D takes, well, a lot of effort, but can happen if the party is stupid and doesn't help each other out.
I love this feature. So, here's a suggestion for how to incorporate it into D&D, or some other game that uses hit points (ans assuming HP represent, in part, luck and ability to dodge, not just structural integrity):
When a character is down to 0 hp, he is incapcitated, and can't do anything. Additionally, he must make a save (vs. Death Ray, or DC 20 Fortitude, or whatever fits the edition) or suffer an ongoing detrimental condition (-2 on all rolls, or perhaps a Negative Level), until the character can rest and get some decent medical attention (takes at least 2 hours and a DC 20 Heal/Treat Injury check, or a Heal spell. Cure spells won't cut it). The effects stack if the character is incapacitated multiple times. Optionally, the third time the effect is applied, the character dies.
If another character gives the incapacitated character a hand up (an attack action), the incapacitated character regains half his lost hit points, although any ongoing conditions remain. Characters cannot be given a hand up in this way until they have been down to 0 hp.
This means that a party can work without a dedicated healer character, but benefits from having one, as the healer can help stave off incapacitation, and thus saves to avoid bad effects, and can help reverse those effects when they occur. Meanwhile, non-dedicated healers will have to, occasionally, help their fellows out.
Similar systems could be applied to paralysis, hypnotism, being chucked off ledges, and suchlike, making each easily fixed by a fellow party member, but forcing a save against some on-going detrimental effect.